In chemistry class, the girl to boy ratio is $7$ to $2$. If there are a total of $36$ students, how many boys are there?
A ratio of $7$ girls to $2$ boys means that a set of $9$ students will have $7$ girls and $2$ boys. A class of $36$ students has $4$ sets of $9$ students. Because we know that there are $2$ boys in each set of $9$ students, the class must have $4$ groups of $2$ boys each. There is a total of $8$ boys in chemistry class.